Cancer, polio shots not linked, study says

By André Picard, Globe and Mail

It was a story with a chilling science-fiction quality to it: Millions of children vaccinated against polio in the 1950s and 1960s were also contaminated with a monkey virus that left them at risk of developing a rare form of lung cancer.

The problem is there is no scientific evidence of a connection, according to research published in today's edition of the Journal of the National Cancer Institute.

Howard Strickler, a professor of epidemiology at the Albert Einstein College of Medicine in New York, found that the rate of pleural mesothelioma, a form of lung cancer normally associated with exposure to asbestos, rose markedly from 1975 to 1997.

But virtually all the increase was among men over the age of 75, a group that did not receive the polio vaccine.

Among the people who were exposed to simian virus 40 (SV40) through vaccination, the incidence rate was unchanged.

"Thus, after almost 40 years of follow-up, U.S. cancer incidence data have not shown an increased incidence of pleural mesothelioma among the birth cohorts that were exposed to SV40-contaminated polio vaccine," Dr. Strickler said.

More important, he said, is that in the younger age group there are six times as many men with the rare lung cancer as there are women, despite the fact that males and females were both vaccinated against polio.

About seven million Canadian children received the polio vaccine from 1955 to 1961.

At the time, the vaccine was cultured from cells taken from the kidneys of rhesus monkeys, and some batches were contaminated with SV40.

In the late 1990s, SV40 was discovered in a number of tumours of people suffering from rare forms of lung cancer and brain cancer. Combined with research that showed hamsters exposed to SV40 developed cancer, this led to speculation that the polio vaccine could cause cancer.

The new research, however, suggests that there is no direct link.

Rather, the rise in cases of pleural mesothelioma is likely related to the aging of people who were heavily exposed to asbestos.

About 8,000 cases of pleural mesothelioma a year are reported in Canada.

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